This invention relates to an elastically stretchable composite sheet comprising a stretchable elastic layer and a stretchable inelastic layer bonded to each other and a process for making the elastically stretchable composite sheet.
PCT Japanese Patent Application Publication No. 1996-504693A describes a multilayered elastic sheet-like structure comprising a rubber-based elastic layer and an inelastic fibrous layer. This sheet-like structure of prior art is obtained by a process comprising steps of placing these rubber-based elastic layer and inelastic fibrous layer upon each other, melting them together or bonded them to each other, stretching them by 100xcx9c200% and then relaxing them. The rubber-based elastic layer is formed with a film or the like and the inelastic fibrous layer is formed with a web made from long fibers such as a spun bond or melt blown fiber web.
According to the prior art as disclosed in the Publication, if it is intended to form the inelastic fibrous layer with, for example, long fibers of polypropylene, a stretch ratio of polypropylene in the step of melt spinning should be limited to a value as low as possible in order that these long fibers can be stretched together with the elastic layer by 100xcx9c200%. This is because that a high stretch ratio of polypropylene would promote crystallization of polypropylene which would, in turn, make it impossible to stretch this inelastic fibrous layer together with the elastic layer at a desired high stretch ratio in the subsequent step. The stretch ratio thus limited in the step of melt spinning will necessarily make it impossible to use the fibers of a desired small diameter. With a disadvantageous consequence, the resultant fibers will give a wearer of the sanitary article using such fibers a touch less than the article using the fibers of appropriately small diameter. In addition, if it is intended to obtain a multilayered elastic sheet-like structure including a bulky inelastic fibrous layer, the fiber having its diameter as small as possible may be used to improve its bulkiness and furthermore to reduce a material cost. However, such advantage can be not obtained so far as the fiber diameter tends to be large.
It is an object of this invention to provide an elastically stretchable sheet-like structure comprising an elastic layer and an inelastic fibrous layer formed with fibers each having a relatively small diameter.
According to one aspect of this invention, there is provided an elastically stretchable composite sheet comprising an elastic layer, the elastic layer being elastically stretchable at least in one direction, and an inelastic layer of fibers, the inelastic layer being inelastically stretchable in the one direction and bonded to at least one surface of the elastic layer and, according to another aspect of this invention, there is provided a process for making such an elastically stretchable composite sheet.
The elastically stretchable composite sheet and the process for making the composite sheet further comprise at least 80% by weight of said fibers including thermoplastic synthetic fiber containing lubricant of 0.1xcx9c5.0% by weight.
The elastically stretchable composite sheet according to this invention uses the fibers containing the lubricant as the stretchable fibers which can be stretched at a ratio sufficiently higher than in the case of the fiber contains no lubricant to reduce the fiber-diameter and thereby to provide the composite sheet with a desired comfortable touch. The thermoplastic synthetic resin as raw material for the stretchable fiber has a fluidity improved by addition of the lubricant and makes it possible to set the nozzle temperature of the extruders at a relatively low level. This facilitates, in turn, the fiber discharged from the extruders to be cooled. In this way, a cost for operation of the extruders is reduced and a productivity of the stretchable fibers is improved.